This paper reports on an experimental study motivated by the issue of vortex formation in fuel tanks of liquid propulsion rockets. In this study, vortex funnel (vortex-air core) formation during draining of liquids from cylindrical tanks is suppressed by means of a simple, yet effective method of controlling or adjusting the size of the base drain port. This is particularly relevant in spacecraft and rocket applications where suppression of such vortex-air core is very much warranted because of the possible drain port blockage they cause and the consequent adverse impact (of vortices) on the generation of propulsive thrust. It is found that in the range of rotational speeds provided to the liquid column (between 120 and 200 rpm) in a cylindrical tank, for d/D∼0.03 (where D is the tank diameter held constant in the study, and d is the port diameter that is varied in the experiments), vortex funnel formation is completely eliminated for concentric drain ports. For eccentric ports, this occurs at a s...

A series of reduced-order numerical simulations on a specific bluff body type (v-gutters) in a subsonic duct flow is performed to assess the unsteady wake dynamics. Two of the v-gutter's geometrical parameters are varied: the v-gutter's base angle (θ) and the size of a slit (ξ) at the leading-edge of the v-gutter. Turbulent flow kinematics and pressure field are analyzed to evaluate the unsteadiness at a freestream Mach number of M∞=0.25 and a freestream Reynolds number based on bluff body's transverse length (L = 17.8 mm) of ReL=0.1×106. Five v-gutter angles are considered (θ, rad=π/6,π/4,π/3,5π/12,π/2) and three slit sizes (ξ, mm =0,0.25,0.5) are considered only for a particular θ=[π/6]. In general, high fluctuations in velocity and pressure are seen for the bluffest body in consideration (θ=π/2) with higher drag (cd) and total pressure loss (Δp0). However, bluffer bodies produce periodic shedding structures that promote flow mixing. On the other hand, the presence of a slit on a streamlined body (θ=π/6) tends to efficiently stabilize the wake and thus producing almost a periodic shedding structure with lower cd and Δp0. For θ=[π/6], broadened spectra in vortex shedding are seen with a peak at [fL/u∞]∼0.08. For θ≥[π/4], a dominant discrete shedding frequency is seen with a gradual spectral decay. Similarly, the effects of ξ on the θ=[π/6] case produce a discrete shedding frequency instead of a broadened one, as seen in the cases of θ≥[π/4]. The shedding frequency increases to a maximum of [fL/u∞]∼0.26 for the maximum slit size of ξ=0.5 mm. From the analysis of the x–t diagram and the modal analysis of vorticity and velocity magnitude in the wake, the peaks are indeed found to agree with the spectral analysis. More insights on the shedding vortices, momentum deficit in the wake, varying energy contents in the flow field, and the dominant spatiotemporal structures are also provided.

Chevron nozzles, which are characterized by the serrations at the nozzle exit, are widely used for suppressing jet noise in aircraft engines. The noise suppression is accomplished by the enhanced mixing of the exhaust streams, which, in turn, is a result of the streamwise vorticity induced by the serrations. The present study focuses on the numerical modeling of the acoustic field in a compressible jet issuing from a chevron nozzle at a Mach number of 0.8. The study evaluates the effectiveness of turbulence modeling approaches of Large Eddy Simulation and Detached Eddy Simulation methods and compares them with the less computationally intensive Unsteady Reynolds Averaged Navier–Stokes (URANS) formulation. The Ffowcs Williams–Hawkings noise model was used to predict the overall sound pressure level in the far field. The LES predictions of the acoustic signature were found to match well with the experimental data, whereas the URANS model grossly underpredicted the sound pressure levels in the compressible jet flow field.

Film cooling as applied to rocket nozzles is analyzed numerically with emphasis on the assessment of the effect of the mixing of coolant with the hot stream. Cooling performance, as characterized by cooling effectiveness, is studied for three different coolants in the three-dimensional, turbulent flow field of a supersonic convergent-divergent nozzle operating with a hot stream temperature of 2500 K over a range of blowing ratios. The coolant stream is injected tangentially into the mainstream using a diffuser-type injector. Parameters influencing the effectiveness, such as coolant injector configuration and mixing layer, are analyzed. Thermal and species mixing between the coolant and the mainstream are investigated with regard to their impact on cooling effectiveness. The results obtained provide insight into the film cooling performance of the gases and the heat transfer characteristics associated with these three gases. An injector taper angle of 30° results in the most effective cooling among the configurations considered (0°, 15°, 30° and 45°). Mixing of the coolant with the hot stream is examined based on the distributions of velocity, temperature and species. The higher values of cooling effectiveness for Helium are attributed to its thermophysical properties and the reduced rate of mixing with the hot stream. The results further indicate that through optimization of the blowing ratio and the coolant injector configuration, the film cooling effectiveness can be substantially improved.

In this study, numerical simulations have been carried out to analyze the effect of convective heat transfer on flow separation occurring in a DLP-PAR nozzle. Heat transfer coefficient (0, 200 and 1000 w/m²K) was applied to the nozzle wall to incorporate the cooling effect for different gas inlet temperatures ranging from 1000 to 1500 K. The impact of the cooling effect was analyzed based on nozzle wall temperature and wall static pressure. The wall static pressure distribution also characterizes movement of the separation point. For an inlet temperature of 1000 K, a detailed heat transfer study was carried out for four different nozzle pressure ratios (14, 22, 30 and 40). Significant amount of heat transfer was observed for pressure ratio 14, which in turn had an impact on flow separation. The wall cooling resulted in a shift of the point of separation towards the nozzle exit. For the nozzle pressure ratio of 14, this shift was by about 8.8%, indicating that the flow separation can be delayed by way of cooling for the considered inlet temperature. For higher inlet temperatures, the effect of heat transfer on flow separation seems to be negligible. The current study concludes that the separation point can be controlled by convective cooling for inlet gas temperatures below 1500 K so that the optimal performance of the nozzle can be achieved.